1. Field of the Invention
The present invention relates to an optical system alternating image capture of a local scene in which the optical system is located and projection of an aerial image by reflection in the optical system, for real time applications such as videoconferences, multimedia or virtual reality.
2. Description of the Prior Art
An aerial image is perceived in a stable and unique plane in space. When it is perceived in that space, the aerial image reproduces in its entirety and with high definition an image of an object via an optical system. In geometrical optics, an aerial image means a real image that is not formed on a screen.
In the prior art, communication installations linking two optical systems employ the generation of aerial images by reflection in order to produce a stereoscopic effect resulting from the perception by an observer of two images superposed on two planes in space via a semi-reflecting plate. The semi-reflecting plate enables a camera to capture an image in the direction of the observer and also enables the observer to view an image by reflection in that same direction. One such communication installation is described in the international patent application WO 01/11880.
These communication installations use the concepts of a “client station” intended for a group of persons and an individual “operator station” to extract the image of an object under particular shooting conditions. A monochrome background behind the object generally facilitates extraction of the image of the object from the operator station and the extracted image of the object is transmitted to the client station, which displays an aerial image of the viewed object for the group of persons. An image captured by the client station is transmitted to the operator station, which displays only the captured image and not the extracted image of the object. The camera is disposed between the semi-reflecting plate and the background of the scene. The camera is therefore not hidden by any device and always remains visible to the observer.
These communication installations are therefore asymmetrical because the functions of the client station and the operator station are different.
Moreover, each optical system is bulky and necessitates a spacious place for its installation.
FIG. 1 illustrates an optical system for aerial image generation by reflection. The system comprises a parabolic mirror MP, a first screen EC1, for example of the cathode ray tube screen type, and a semi-reflecting plate LS adapted to transfer an image of an object coming from the first screen EC1 to a plane PI in space, in the direction of an observer OB, via a lens LEN. The lens is adapted to cause a light beam coming from the first screen EC1 to converge to form a high-definition aerial image IA in the plane PI of the space.
The effect of the aerial image IA perceived in the plane PI by the observer OB floating is accentuated by the display of a second image representing a background scene on a second screen EC2 located in the background.
This kind of optical system does not provide observer image capture and therefore cannot be used for real time applications such as videoconferences.